Construction and characterization of an infectious cDNA clone of enterovirus type 71 subgenotype C4

Construction of an infectious clone for enterovirus A89 and mutagenesis analysis of viral infection and cell binding

Enterovirus A89 (EV-A89) is an unconventional strain belonging to the Enterovirus A species. Limited research has been conducted on EV-A89, leaving its biological and pathogenic properties unclear. Developing reverse genetic tools for EV-A89 would help to unravel its infection mechanisms and aid in the development of vaccines and anti-viral drugs. In this study, an infectious clone for EV-A89 was successfully constructed and recombinant enterovirus A89 (rEV-A89) was generated. The rEV-A89 exhibited similar characteristics such as growth curve, plaque morphology, and dsRNA expression with parental strain. Four amino acid substitutions were identified in the EV-A89 capsid, which were found to enhance viral infection. Mechanistic studies revealed that these substitutions increased the virus's cell-binding ability. Establishing reverse genetic tools for EV-A89 will significantly contribute to understanding viral infection and developing anti-viral strategies.IMPORTANCEEnterovirus A species contain many human pathogens and have been classified into conventional cluster and unconventional cluster. Most of the research focuses on various conventional members, while understanding of the life cycle and infection characteristics of unconventional viruses is still very limited. In our study, we constructed the infectious cDNA clone and single-round infectious particles for the unconventional EV-A89, allowing us to investigate the biological properties of recombinant viruses. Moreover, we identified key amino acids residues that facilitate EV-A89 infection and elucidate their roles in enhancing viral binding to host cells. The establishment of the reverse genetics system will greatly facilitate future study on the life cycle of EV-A89 and contribute to the development of prophylactic vaccines and anti-viral drugs.

Proteomic and phosphoproteomic analysis of responses to enterovirus A71 infection reveals novel targets for antiviral and viral replication

Hand, foot, and mouth disease (HFMD) is a common infectious disease in infants and children, especially those under five years of age. EV-A71 is a common pathogen that causes HFMD and the primary pathogen leading to severe or fatal HFMD, which is characterized by neurological complications. However, the underlying mechanisms of EV-A71 pathogenesis remain largely unknown. In this report, we used proteomic and phosphorylated proteomic methods to characterize the proteome and phosphoproteome profiles of EV-A71-infected human neuroblastoma SK-N-SH cells. More than 7744 host proteins and 10069 phosphorylation modification sites were successfully quantified. Among them, 974 proteins and 3648 phosphorylation modification sites were regulated significantly during EV-A71 infection. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis revealed that EV-A71 altered cell biological processes, including protein synthesis, RNA splicing and metabolism in SK-N-SH cells. Notably, based on the prediction of upregulated kinases during EV-A71 infection, we identified specific kinase inhibitors approved by the FDA, with ceralasertib, bosutinib, flavin mononucleotide, minocycline, pimasertib and acetylcysteine inhibiting EV-A71 infection. Finally, EV-A71 proteins were found to be phosphorylated during infection, with one site (S184 on 3D polymerase) observed to be crucial for viral replication because a S184A mutation knocked out viral replication. The results improve our understanding of the host response to EV-A71 infection of neuroblastoma cells and provide potential targets for developing anti-EV-A71 strategies.

Enterovirus A71 Promotes Exosome Secretion by the Nonstructural Protein 3A Interacting with Rab27a

Exosomes are small membrane-bound vesicles which are intraluminal vesicles (ILVs) secreted to the extracellular space after multivesicular bodies (MVBs) fuse with the plasma membrane. Although it is known that exosomes play a multitude of roles during viral infection, the mechanism that regulates their secretion during viral infection is unknown. Here, we found that enterovirus A71 (EV-A71) infection increased exosome secretion both in vivo and in vitro. Importantly, the expression of nonstructural protein 3A was sufficient to promote exosome secretion, while a mutation affecting the amino acid 18 position abrogated this effect, without changing the size of exosomes in vivo or in vitro. Transmission electron microscopy (TEM) analysis revealed that 3A decreases the number of MVBs and ILVs in vivo and in vitro, which suggested 3A may boost the fusion between MVBs and the plasma membrane. Furthermore, we demonstrated that an interaction between 3A and the small GTPase protein, Rab27a, protected Rab27a from ubiquitination, resulted in increasing exosome release. Data indicated a novel mechanism by which EV-A71 3A modifies exosome secretion during viral infection. IMPORTANCE Research has shown that viral infection impacts exosome secretion, but its regulation mechanisms remain poorly understood. Nonstructural protein 3A of EV-A71 interacts with many host factors and is involved in the remodeling of cellular membranes. In this investigation, we applied exogenous expression of 3A protein for exploring its regulation on exosome secretion and utilized immunoprecipitation combined with proteomics approaches to identify 3A-interacting factors. Our results demonstrate that 3A protein upregulates the release of the exosomes and that the 3A mutant strain of EV-A71 induce less exosome release compared with the EV-A71 wild type. Viral 3A protein interacts with the host factor Rab27a to prevent it from being ubiquitinated, which in turn improves exosome secretion both in vitro and in vivo. EV-A71 3A protein is a novel viral factor in the control of exosome production.

Novel strategies for the development of hand, foot, and mouth disease vaccines and antiviral therapies

INTRODUCTION

Hand, foot, and mouth disease (HFMD) poses a great threat to young children in the Asia-Pacific region. HFMD is usually caused by enterovirus A, and infection with enterovirus A71 (EV-A71) is particularly associated with severe complications. However, coxsackievirus CV-A16, CV-A6, and CV-A10 pandemics have been observed in recent HFMD outbreaks. Inactivated monovalent EV-A71 vaccines are available to prevent EV-A71 infection; however, they cannot prevent infections by non-EV-A71 enteroviruses. Anti-enteroviral drugs are still in the developmental stage. Application of novel strategies will facilitate the development of new therapies against these emerging HFMD-associated enteroviruses.

AREAS COVERED

The authors highlight the current approaches for anti-enterovirus therapeutic development and discuss the application of these novel strategies for the discovery of vaccines and antiviral drugs for enteroviruses.

EXPERT OPINION

The maturation of DNA/RNA vaccine technology could be applied for rapid and robust development of multivalent enterovirus vaccines. Structure biology and neutralization antibody studies decipher the immunodominant sites of enteroviruses for vaccine design. Nucleotide aptamer library screening is a novel, fast, and cost-effective strategy for the development of antiviral agents. Animal models carrying viral receptors and attachment factors are required for enterovirus study and vaccine/antiviral development. Currently developed antivirals require effectiveness evaluation in clinical trials.

Construction and characterization of an infectious cDNA clone of enterovirus 71: a rapid method for rescuing infectious virus based on stable cells expressing T7 polymerase

Enterovirus 71 (EV71) is a causative agent of hand, foot and, mouth disease (HFMD) in young children. It is valuable for virologists to develop a fast method to rescue infectious virus from a viral cDNA clone. Here, we report a method for rapid rescue of infectious EV71 by using cells expressing T7 polymerase. The full-length EV71 genome was amplified in one step by long-distance PCR with a T7 promoter at the 5' end, and the T7 polymerase gene was cloned into a lentivirus vector for construction of a stable cell line expressing T7 polymerase. The infectious virus was rapidly and efficiently rescued by single transfection of cells with the infectious cDNA clone. Further experiments showed that the rescued virus had characteristics similar to those of the parental virus. This method circumvented the difficulty in performing in vitro transcription of a long linear DNA to obtain high-quality RNA. The construction of the viral cDNA clone and the fast rescue of the infectious virus will greatly benefit future investigations.

Construction and characterization of an infectious cDNA clone of coxsackievirus A 10

Background

Coxsackievirus A10 (CA10) constitutes one of the four major pathogens causing hand, foot and mouth disease in infants. Infectious clones are of great importance for studying viral gene functions and pathogenic mechanism. However, there is no report on the construction of CA10 infectious clones.

Methods

The whole genome of CA10 derived from a clinical isolate was amplified into two fragments and ligated into a linearized plasmid vector in one step by In-Fusion Cloning. The obtained CA10 cDNA clones and plasmids encoding T7 RNA polymerase were co-transfected into 293 T cells to rescue CA10 virus. The rescued virus was identified by SDS-PAGE, Western blotting and transmission electron microscopic. One-day-old ICR mice were intracerebrally inoculated with the CA10 virus and clinical symptoms were observed. Multiple tissues of moribund mice were harvested for analysis of pathogenic changes and viral distribution by using H&E staining, real-time PCR and immunohistochemical staining.

Results

CA10 viruses were rescued from the constructed cDNA clone and reached a maximum titer of 10^8.125TCID₅₀/mL after one generation in RD cells. The virus exhibited similar physical and chemical properties to those of the parental virus. It also showed high virulence and the ability to induce death of neonatal ICR mice. Severe necrotizing myositis, intestinal villus interstitial edema and severe alveolar shrinkage were observed in infected mice. The viral antigen and the maximum amount of viral RNA were detected in limb skeletal muscles, which suggested that the limb skeletal muscles were the most likely site of viral replication.

Conclusion

Infectious clones of CA10 were successfully constructed for the first time, which will facilitate the establishment of standardized neonatal mouse models infected with CA10 for the evaluation of vaccines and antiviral drugs, as well as preservation and sharing of model strains.

A Reverse Genetics System for Cypovirus Based on a Bacmid Expressing T7 RNA Polymerase

Dendrolimus punctatus cypovirus (DpCPV), belonging to the genus Cypovirus within the family Reoviridae, is considered the most destructive pest of pine forests worldwide. DpCPV has a genome consisting of 10 linear double-stranded RNA segments. To establish a reverse genetics system, we cloned cDNAs encoding the 10 genomic segments of DpCPV into three reverse genetics vectors in which each segment was transcribed under the control of a T7 RNA polymerase promoter and terminator tagged with a hepatitis delta virus ribozyme sequence. We also constructed a vp80-knockout Autographa californica multiple nucleopolyhedrovirus bacmid to express a T7 RNA polymerase codon-optimized for Sf9 cells. Following transfection of Sf9 cells with the three vectors and the bacmid, occlusion bodies (OBs) with the typical morphology of cypovirus polyhedra were observed by optical microscopy. The rescue system was verified by incorporation of a HindIII restriction enzyme site null mutant of the 9th genomic segment. Furthermore, when we co-transfected Sf9 cells with the reverse genetics vectors, the bacmid, and an additional vector bearing an egfp gene flanked with the 5′ and 3′ untranslated regions of the 10th genomic segment, aggregated green fluorescence co-localizing with the OBs was observed. The rescued OBs were able to infect Spodopetra exigua larvae, although their infectivity was significantly lower than that of wild-type DpCPV. This reverse genetics system for DpCPV could be used to explore viral replication and pathogenesis and to facilitate the development of novel bio-insecticides and expression systems for exogenous proteins.

A reverse genetics system for enterovirus D68 using human RNA polymerase I

Human enterovirus D68 (EV-D68) is a highly contagious virus, which causes respiratory tract infections. However, no effective vaccines are currently available for controlling EV-D68 infection. Here, we developed a reverse genetics system to recover EV-D68 minireplicons and infectious EV-D68 from transfected plasmids using the RNA polymerase I (Pol I) promoter. The EV-D68 minireplicons contained the luciferase reporter gene, which flanked by the non-coding regions of the EV-D68 RNA. The luciferase signals could be detected in cells after transfection and Pol I promoter-mediated luciferase signal was significantly stronger than that mediated by the T7 promoter. Furthermore, recombinant viruses were generated by transfecting plasmids that contained the genomic RNA segments of EV-D68, under the control of Pol I promoter into 293T cells or RD cells. On plaque morphology and growth kinetics, the rescued virus and parental virus were indistinguishable. In addition, we showed that the G394C mutation disrupts the viral 5'-UTR structure and suppresses the viral cap-independent translation. This reverse genetics system for EV-D68 recovery can greatly facilitate research into EV-D68 biology. Moreover, this system could accelerate the development of EV-D68 vaccines and anti-EV-D68 drugs.

The Golgi protein ACBD3 facilitates Enterovirus 71 replication by interacting with 3A

Enterovirus 71 (EV71) is a human pathogen that causes hand, foot, mouth disease and neurological complications. Although EV71, as well as other enteroviruses, initiates a remodeling of intracellular membrane for genomic replication, the regulatory mechanism remains elusive. By screening human cDNA library, we uncover that the Golgi resident protein acyl-coenzyme A binding domain-containing 3 (ACBD3) serves as a target of the 3A protein of EV71. This interaction occurs in cells expressing 3A or infected with EV71. Genetic inhibition or deletion of ACBD3 drastically impairs viral RNA replication and plaque formation. Such defects are corrected upon restoration of ACBD3. In infected cells, EV71 3A redirects ACBD3, to the replication sites. I44A or H54Y substitution in 3A interrupts the binding to ACBD3. As such, viral replication is impeded. These results reveal a mechanism of EV71 replication that involves host ACBD3 for viral replication.

Construction and characterization of an infectious cDNA clone of Echovirus 25

Echovirus 25 (E-25) is a member of the enterovirus family and a common pathogen that induces hand, foot, and mouth disease (HFMD), meningitis, skin rash, and respiratory illnesses. In this study, we constructed and characterized an infectious full-length E-25 cDNA clone derived from the XM0297 strain, which was the first subgenotype D6 strain isolated in Xiamen, China. The 5'-Untranslated Regions (5'-UTR), P3 (3A-3B, 3D) and P3 (3C) regions of this E-25 (XM0297) strain were highly similar to EV-B77, E-16 and E-13, respectively. Our data demonstrate that the rescued E-25 viruses exhibited similar growth kinetics to the prototype virus strain XM0297. We observed the rescued viral particles using transmission electron microscope (TEM) and found them to possess an icosahedral structure, with a diameter of approximately 30 nm. The cross neutralization test demonstrated that the E-25 (XM0297) strain immune serum could not neutralize EV-A71, CV-A16 or CV-B3; likewise, the EV-A71 and CV-A16 immune serum could not neutralize E-25 (XM0297). The availability of this infectious clone will greatly enhance future virological investigations and possible vaccine development against E-25.